A hydraulic gear pump immersed in its own reservoir delivers pressurised oil to the vane-type 90° actuator via the control box, which contains non-return valves and solenoid valves to direct the flow into the actuator; with cam operated limit switches to control travel and (optionally) signal position to the user. The unpressurised side of the actuator is connected to the reservoir, so there is no net transfer of oil from reservoir to actuator.

The pump and its motor run entirely on precision ball bearings, so that the friction and motor size can be minimised and life maximised; the efficiency resulting from this reduces the heating effect and allows 100% rating.

A pressure release valve is built into the pump so that if the actuator load becomes jammed the torque is limited and dangerous over pressures or motor stalls are avoided.

Fail-safe spring return action uses our reliable low-stress-range sealed clock-type spring unit mounted coaxially with the actuator, together with a fail-open solenoid valve, to ensure reliable positioning when power is not supplied to the unit.

A high flow external dump valve can be fitted to allow very rapid spring-driven action. Double-acting models are supplied with solenoids arranged to give position locking when power is disconnected.

An optional manual by-pass valve is available to allow manual override movement of a double acting model when power is disconnected.

The interface between pump/reservoir unit and the control box allows mounting of the pump in different orientations at 90° to each other, so that the motor can be kept above the reservoir whether the actuator output axis is horizontal or vertical.

External electrical connections are all made via a single accessible connector block in the control box, with the simplest possible switching needed to drive the unit. Two conduit entries are available, to allow easy separate connection of power and signal lines (if used). All internal wiring is connected via a central connector and fuse board and the actuator is protected from supply surges by a metal oxide varistor suppressor.


  • Low wear from low-stress, low pressure gear pump driving simple vane actuator gives long life.
  • Runs all day and all night without overheating.
  • If load jams, pressure release valve prevents overtorque or motor stalling.
  • Environmentally sealed enclosure to IP65/NEMA 4, with tough epoxy paint on robust cast metal to resist outdoor environments.
  • Compact, powerful single unit with no external pipes or wires.
  • Six models – wide torque/speed range – each model can be specified as failsafe spring-return or high-torque double acting, on-off or modulating.


  • Fail safe uses simple integral spring unit working against electrohydraulic vane actuator – no batteries or gas bottles .
  • Double acting also available for high torque conventional electric actuator options.
  • Integral positioner option drives to and holds any angle from 0° to 90° in response to 4-20mA signal.
  • Auxiliary limit switches optionally available for external signalling of position by user.
  • Fail locked double acting – Solenoid arrangement gives position locking on power disconnection – manual bypass valve can be fitted for manual override of fail-locked actuator.
  • Local isolation switches option – Switch between local and remote control, with clockwise and anti-clockwise switches available on unit.
  • Low temperature option – A heater and jacket assembly can now be supplied to further increase the EHD operating temperature range.
  • Silicone free oil versions available – A mineral oil is used instead of the standard silicone oil (temperature restrictions apply).
  • Integral options and add-on units

– 4-20mA transducer for independent position feedback.

– internal feedback potentiometer for connection to user’s external circuit.

– split range positioner signals (4-20mA and 12-20mA signals).

  • Clear cone – High visibility monitor available.
  • ISO/DIN female drive options available.

Zjaan Haarhoff
Tel. +27 11 708 6455

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